Abstract
The current climate issues gave rise to the emergence of low carbon cements, in particular belite calcium sulfoaluminate cements (CSAB). These cements are quite recent and the literature is limited; only a few studies have been published on CSAB in the presence of admixtures, even though these are key components of modern concrete. Indeed, concrete fresh state mainly depends on their use, for example plasticizers (or superplasticizers) allow the control of workability without the addition of extra-water, or setting regulators such as retarders. Therefore, the purpose of this thesis work is to give a better understanding of their hydration, without and with admixtures, and from the first minutes to 6 months of hydration. Anhydrous materials (clinkers and anhydrite) were first characterized, then an optimum anhydrite content was determined for each of the three clinkers. The resulting cements were studied at short term (isotherm microcalorimetry, XRD, ICP), then at longer ages (XRD), when the phase assemblage was correlated to the compressive strength. Those mainly depend on belite hydration products. The effect of different admixtures (a polycarboxylate PC, a lignosulfonate LS and borax B) on the hydration and rheological properties of CSAB cements was studied. They fluidize cement pastes thanks to both mesostructural rearrangement and modification of ettringite precipitation, which are closely related parameters. LS and B efficiency depends on the cement nature, dosage must be increased for those which reactivity is quicker. Moreover, there is a dosage from which their effect changes from accelerating to retarding the hydration.